The Collaborative International Dictionary of English v.0.48:

Exculpate \Ex*cul"pate\, v. t. [imp. & p. p. Exculpated, p.
   pr. & vb. n.. Exculpating (?).] [L. ex out + culpatus, p.
   p. of culpare to find fault with, to blame, culpa fault. See
   Culpable.]
   To clear from alleged fault or guilt; to prove to be
   guiltless; to relieve of blame; to acquit.
   [1913 Webster]

         He exculpated himself from being the author of the
         heroic epistle.                          --Mason.
   [1913 Webster]

         I exculpate him further for his writing against me.
                                                  --Milman.

   Syn: To exonerate; absolve; clear; acquit; excuse; vindicate;
        justify.
        [1913 Webster]

WordNet (r) 3.0 (2006):

exculpate
    v 1: pronounce not guilty of criminal charges; "The suspect was
         cleared of the murder charges" [syn: acquit, assoil,
         clear, discharge, exonerate, exculpate] [ant:
         convict]